Drilling flanges provide an interface to well casing heads for mounting various equipment such as blow-out preventers. A conventional drilling flange is threaded onto the casing head until a shoulder within the drilling flange makes contact with the casing head end face. An elastomeric O-ring seals the drilling-flange/casing-head interface.
The standard 8-round thread used in oil wells is a tapered thread. Tapered threads are typically threaded together until the inner and outer tapers are tightly engaged to form a secure, and usually leak free, connection. However, the drilling flange is designed not to fully engage the casing head thread. The reason behind this design philosophy is that if the drilling flange inner thread were to fully engage the casing head outer thread prior to the formation of the tightly sealed casing head end face/drilling-flange interface, a tightly sealed interface would not result. Since the 8-round thread is not fully engaged, a sloppy thread fit exists between the drilling flange and the casing head. This allows for destructive movement of the threads during use, especially during the highly vibrating drilling process, resulting in the rapid wear of both threads. Another problem associated with conventional drilling flanges is undue wear on both the casing head and the drilling flange threads due to frequent installations and removals.
While the prior art discloses various systems for providing an interface to a well, including drilling flanges, none disclose a two-piece drilling flange with a technique for assuring a tight seal and for fully engaging the casing head 8-round thread, as described herein.